U.S. patent number 4,477,523 [Application Number 06/536,825] was granted by the patent office on 1984-10-16 for flame retardant crosslinked polyolefin insulation material.
This patent grant is currently assigned to National Distillers and Chemical Corporation. Invention is credited to James W. Biggs, Melvin F. Maringer.
United States Patent |
4,477,523 |
Biggs , et al. |
* October 16, 1984 |
Flame retardant crosslinked polyolefin insulation material
Abstract
A filled crosslinked polymeric composition of ethylene-vinyl
ester copolymer which has a significant degree of flame retardancy
by inclusion of a dual lubricant system which includes a fatty acid
and an alkylene-bis-amide.
Inventors: |
Biggs; James W. (Lebanon,
OH), Maringer; Melvin F. (Cincinnati, OH) |
Assignee: |
National Distillers and Chemical
Corporation (New York, NY)
|
[*] Notice: |
The portion of the term of this patent
subsequent to September 14, 1999 has been disclaimed. |
Family
ID: |
27005475 |
Appl.
No.: |
06/536,825 |
Filed: |
September 28, 1983 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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371688 |
Apr 26, 1982 |
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Current U.S.
Class: |
428/389; 428/391;
523/212; 524/228; 524/229; 524/232; 524/264; 524/288; 524/300;
524/303; 524/305; 524/322; 524/563; 524/87; 524/94 |
Current CPC
Class: |
C08K
3/2279 (20130101); C08K 5/20 (20130101); C08K
5/54 (20130101); H01B 3/441 (20130101); C08K
5/09 (20130101); C08K 3/2279 (20130101); C08L
23/08 (20130101); C08K 5/09 (20130101); C08L
23/08 (20130101); C08K 5/20 (20130101); C08L
23/08 (20130101); C08K 5/54 (20130101); C08L
23/08 (20130101); Y10T 428/2962 (20150115); Y10T
428/2958 (20150115) |
Current International
Class: |
C08K
3/00 (20060101); C08K 3/22 (20060101); C08K
5/00 (20060101); C08K 5/20 (20060101); C08K
5/09 (20060101); C08K 5/54 (20060101); H01B
3/44 (20060101); C08K 005/38 (); C08K 005/09 ();
C08K 003/22 (); C08L 023/08 () |
Field of
Search: |
;524/87,228,229,232,94,288,300,303,305,322,264,563
;428/389,391 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0002814 |
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Feb 1967 |
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JP |
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0117547 |
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Sep 1979 |
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JP |
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0078048 |
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Jun 1980 |
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JP |
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Other References
Derwent Abst. 22080E/12 BE890270; 22079E/12 BE890269, Published
3-8-82. .
Derwent Abst. 70694Y/40 (9-77) BE852991 Nat. Distillers. .
Derwent Abst. 67910C/39 (9-80) DT2909498 BASF AG. .
Derwent Abst. 96744X/52 (11-76) J51128194 Sumitomo. .
Derwent Abst. 68609B/38 (9-79) GB2016016 Nat. Distillers. .
Derwent Abst. 52283D/29 (5-81) J56062842 Sekisui Chemi. .
Derwent Abst. 14389E/08 (1-82) J57005752 Mitsubishi. .
Derwent Abst. 52282D/29 (5-81) J56062841 Sekisui Chemi..
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Primary Examiner: Lilling; Herbert J.
Attorney, Agent or Firm: Tremain; Kenneth D.
Parent Case Text
This is a continuation of co-pending application Ser. No. 371,688
filed Apr. 26, 1982, now abandoned.
Claims
What is claimed is:
1. A crosslinkable polymeric composition having improved flame
retardancy comprising:
(a) a copolymer of ethylene and a vinyl ester of a C.sub.2 -C.sub.6
aliphatic carboxylic acid, a C.sub.1 -C.sub.6 alkyl acrylate or
C.sub.1 -C.sub.6 alkyl methacrylate,
(b) from 80 to 400 parts of hydrated inorganic filler per 100 parts
of copolymer,
(c) 0.4 to 8 parts of an alkoxysilane per 100 parts of hydrated
inorganic filler, and
(d) a flame-retardant component containing a dual lubricant system
comprising a fatty acid having from 8 to 25 carbon atoms and an
alkylene-bis-amide having the general formula: ##STR4## wherein R=a
divalent alkylene radical of from 2 to 8 carbon atoms; and
R'= ##STR5## wherein R.sup.2 is an aliphatic radical having from 8
to 25 carbon atoms, a halogenated flame retardant and, optionally,
antimony trioxide.
2. In a crosslinked polymeric composition having significant flame
retardancy which comprises:
(a) a copolymer of ethylene and a vinyl ester of a C.sub.2 -C.sub.6
aliphatic carboxylic acid, a C.sub.1 -C.sub.6 alkyl acrylate or
C.sub.1 -C.sub.6 alkyl methacrylate,
(b) from about 80 to about 400 parts of hydrated inorganic filler
per 100 parts of copolymer, and
(c) about 0.4 to about 8 parts of an alkoxysilane per 100 parts of
hydrated inorganic filler; the improvement comprising:
(d) a flame-retardant component containing a dual lubricant system
comprising a fatty acid having from 8 to 25 carbon atoms and an
alkylene-bis-amide having the general formula ##STR6## wherein R=a
divalent alkylene radical of from 2 to 8 carbon atoms;
R'= ##STR7## wherein R.sup.2 is an aliphatic radical having from 8
to 25 carbon atoms, a halogenated flame-retardant, and, optionally,
antimony trioxide.
3. The composition of claim 1, wherein said dual lubricant system
is present in an amount of from about 0.1 to about 10 percent by
weight of the total polymeric composition.
4. The composition of claim 3, wherein said dual lubricant system
is present in an amount of from about 0.5 to about 3.0 percent by
weight of the total polymeric composition.
5. The composition of claim 3, wherein the ratio of said fatty acid
to said alkylene-bis-amide is from about 1:1 to about 1:6.
6. The composition of claim 5, wherein said ratio is about 1:3.
7. The composition of claim 3, wherein said fatty acid is lauric
acid.
8. The composition of claim 3, wherein said alkylene-bis-amide is
ethylene-bis-stearamide.
9. The composition of claim 3, wherein said dual lubricant system
comprises lauric acid and ethylene-bis-stearamide.
10. The composition of claim 9, wherein the ratio of said lauric
acid to said ethylene-bis-stearamide is about 1:3.
11. The composition of claims 1, wherein said halogenated flame
retardant is present in an amount of from about 5 to about 30
percent by weight of the total polymeric composition.
12. The composition of claim 5, wherein said halogenated flame
retardant is present in an amount of from about 8 to about 14
percent by weight of the total polymeric composition.
13. The composition of claims 1, wherein said halogenated flame
retardant is selected from the group consisting of
ethylene-bis-tetra-bromophthalimide and deca-bromodiphenyl
oxide.
14. The composition of claims 1, wherein said antimony trioxide is
present in an amount of from about 2 to about 20 percent by weight
of the total polymeric composition.
15. The composition of claim 14, wherein said antimony trioxide is
present in an amount of from about 4 to about 8 percent by weight
of the total polymeric composition.
16. An electrical conductor coated with a uniinsulating layer
comprising the crosslinked polymeric compositions of claim 1.
17. A method of providing flame retardancy to a crosslinkable
polymeric composition comprising:
(a) a copolymer of ethylene and a vinyl ester of a C.sub.2 -C.sub.6
aliphatic carboxylic acid, a C.sub.1 -C.sub.6 alkyl acrylate or
C.sub.1 -C.sub.6 alkyl methacrylate,
(b) from 80 to 400 parts of hydrated inorganic filler per 100 parts
of copolymer, and
(c) 0.4 to 8 parts of an alkoxysilane per 100 parts of hydrated
inorganic filler, by including in said composition a
flame-retardant component comprising a dual lubricant system
comprising a fatty acid having from 8 to 25 carbon atoms and an
alkylene-bis-amide having the general formula: ##STR8## wherein R=a
divalent alkylene radical of from 2 to 8 carbon atoms; and
R'= ##STR9## wherein R.sup.2 is an aliphatic radical having from 8
to 25 carbon atoms, a halogenated flame retardant and, optionally,
antimony trioxide.
18. The method of claim 17, wherein said dual lubricant system is
present in an amount of from about 0.1 to about 10 percent by
weight of the total polymeric composition.
19. The method of claim 18, wherein said dual lubricant system is
present in an amount of from about 0.5 to about 3.0 percent by
weight of the total polymeric composition.
20. The method of claim 18, wherein the ratio of said fatty acid to
said alkylene-bis-amide is from about 1:1 to about 1:6.
21. The method of claim 20, wherein said ratio is about 1:3.
22. The method of claim 17, wherein said fatty acid is lauric
acid.
23. The method of claim 17, wherein said alkylene-bis-amide is
ethylene-bis-stearamide.
24. The method of claim 17, wherein said dual lubricant system
comprises lauric acid and ethylene-bis-stearamide.
25. The composition of claim 24, wherein the ratio of said lauric
acid to said ethylene-bis-stearamide is about 1:3.
26. The method of claim 17, wherein said halogenated flame
retardant is present in an amount of from about 5 to about 30
percent by weight of the total polymeric composition.
27. The method of claim 20, wherein said halogenated flame
retardant is present in an amount of from about 8 to about 14
percent by weight of the total polymeric composition.
28. The method of claim 17, wherein said halogenated flame
retardant is selected from the group consisting of
ethylene-bis-tetrabromophthalimide and deca-bromodiphenyl
oxide.
29. The method of claim 17, wherein said antimony trioxide is
present in an amount of from about 2 to about 20 percent by weight
of the total polymeric composition.
30. The method of claim 29, wherein said antimony trioxide is
present in an amount of from about 4 to about 8 percent by weight
of the total polymeric composition.
Description
BACKGROUND OF THE INVENTION
The present invention relates to cross-linkable polymeric
compositions which exhibit moisture, heat and flame resistance and
which are useful in producing insulated wire and cable as well as
molded products. More particularly, it relates to an ethylene-vinyl
acetate copolymer composition having a high degree of flame
retardancy.
One of the most important areas where fire resistant polymer
compositions find use is in the electrical environment, i.e., where
both insulating and fire resistant properties are sought, most
especially in the area of conductor insulation. At one time,
extrudable compositions available to the wire and cable art were
required, for flame resistance, to contain halogenated polymers
such as chlorinated polyethylene, polyvinyl chloride,
chlorobutadiene, chlorinated paraffin, etc., together with antimony
trioxide, both components being present in sizable quantities.
Alternatively, a coating of chlorosulfonated polyethylene paint was
applied to a non-flame retardant insulating compound which
constituted an additional manufacturing operation.
For certain types of dry transformers, particularly high voltage
transformers, a problem existed in that electrical failures
occurred due to surface creepage of the organic insulating compound
used. The problem was solved through the addition of hydrated
alumina to compositions whose organic binder consisted of butyl
rubber, epoxy resins or polyester resins. However, these
compositions do not possess a balance of excellent extrudability
characteristics, physical and electrical properties, heat
resistance and flame retardance. Such compositions are disclosed in
U.S. Pat. Nos. 2,997,526; 2,997,527 and 2,997,528 to Kessel et al.
The described compositions for such usage have poor tensile
strength, elongation and percent elongation retained after
aging.
Fire retarding polymeric compositions exhibiting, inter alia,
improved moisture and heat resistance consisting essentially of an
intimate mixture of at least one cross-linkable polymer containing
as a major component an ethylene-vinyl acetate copolymer, one or
more silanes and one or more hydrated inorganic fillers have found
wide acceptance in the wire and cable art. Compositions such as
these are disclosed in U.S. Pat. Nos. 3,832,326 and 3,922,442 of
North et al. These patents disclose compositions which contain 80
to 400, preferably 125-140 weight parts of filler per 100 weight
parts of polymer and 0.5 to 5.0 parts of silane per 100 parts of
filler. No specific concentration range of lubricant is disclosed
although 2 parts of calcium stearate per 100 parts of polymer are
utilized in all of the fourteen compositions of the examples.
The prior art polymeric compositions of North et al., exhibit a
balance, of improved physical and electrical properties together
with a high degree of flame and fire retardance. These highly
desirable results are achieved without the use of halogenated
polymers such as polyvinyl chloride and chlorosulfonated
polyethylene, thereby eliminating hydrogen chloride fumes; without
carbon black, thereby permitting its use as colored insulations;
without any flame retardant coatings such as are currently
required, thereby eliminating an additional step in manufacturing
operations when the compositions are used as, e.g., insulating
compounds extruded onto a conductor.
Such compositions find particular use as white (an inherent
property) and colored uniinsulation compositions, which can be
extruded over metal, e.g., copper or aluminum, conductors, to
provide a single layer insulating and jacketing composition which
is rated according to U.L. standards for 90.degree. C. operation,
and in some cases operation at temperatures as high as 125.degree.,
at up to 600 volts.
The insulating compositions of North et al. have found particular
utility in the insulation of switchboard wire, appliance wire, and
automotive wire where a unique combination of superior electrical
properties combined with resistance to the degradative effects of
heat and flame are essential, and where low smoke density and
non-corrosive fumes are desirable.
North et al. contemplate ethylene-vinyl acetate copolymers in their
compositions crosslinked by irradiation with high energy sources or
through the use of chemical crosslinking agents. As has been
observed with other radiation cured polymeric compositions,
radiation cured compositions prepared in accordance with the
disclosures of North et al. have poorer physical strength
properties than their peroxide cured counterparts. The reasons for
this are not fully understood although the precise nature and
amount of the major and minor components in the composition are
thought to be a contributing factor. Several modifications were
made to the peroxide curable product to produce the radiation
curable counterpart. The copolymer in the radiation curable product
has a higher vinyl acetate content and aluminum stearate has been
substituted for the calcium stearate lubricant. Although this has
improved the physical strength of the radiation cured composition
over what it would have been, it is still significantly lower than
the peroxide cured product.
Copending U.S. Ser. No. 185,460, filed Sept. 9, 1980, now U.S. Pat.
No. 4,349,605 describes a radiation cross-linked polymer
composition having improved physical strength properties
substantially similar to a chemically crosslinked counterpart. The
improved physical strength properties are achieved by the use of
increased amounts of silane and the substitution of the lubricant
Mold Wiz for the aluminum stearate lubricant.
Besides the three essential components, other additives can be
incorporated into the compositions of North et al. to provide
certain desireable qualities. Included in these additives are
pigments, antioxidants and stabilizers.
Antioxidants are included to inhibit polymer degradation resulting
from oxidation which proceeds by a free radical chain mechanism.
The antioxidants act either to tie up the peroxy radicals so that
free radicals are incapable of propagating the reaction chain, or
to decompose the hydroperoxides in such a manner that carbonyl
groups and additional free radicals are not formed. The former,
called chainbreaking antioxidants, free radical scavengers, or
inhibitors, usually are hindered phenols, amines, and the like. The
latter, called peroxide decomposers, generally are sulfur compounds
(i.e., mercaptans, sulfides, disulfides, sulfoxides, sulfones,
thiodipropionic acid esters and the like), or metal complexes of
dithiocarbamates and dithiophosphates.
The art also shows stabilizers for synthetic resins such as in U.S.
Pat. No. 4,279,805 which describes an alkylene bis-thioalkanoic
acid amide as a stabilizer, and corrosion inhibitors as, for
example, described in U.S. Pat. No. 4,124,549 to Hashiudo et
al.
Another disclosure, U.S. Pat. No. 4,255,303 to Keogh, shows a
composition for electrical applications having electrical
resistance, tensile strength, and elongation capability which
includes ethylene-vinyl acetate, halogenated flame-retardant,
antimony trioxide, peroxide and zinc stearate. U.S. Pat. No.
4,035,325 to Poppe et al describes a combination in which the
effectiveness of flame retardant combinations of antimony trioxide
and a halogen-containing compounds such as hexabromocyclododecane
(HBCD), chlorinated paraffins, tetrabromophthalic anhydride (TBPA),
and tetrabromoterephthalic acid (TBTA), is purportedly increased by
the addition of certain organometallic compounds which have the
chemical structure of either substituted hydrazines or substituted
3-amino-1,2,4-triazole amides.
By the present invention there is provided a polymeric composition
with a lubricant system which also significantly increases the
flame-retardancy of the composition.
SUMMARY OF THE INVENTION
In accordance with the present invention, it has been found that a
significant flame-retardant quality can be achieved in ethylene
copolymer (particularly ethylene-vinyl acetate copolymers)
compositions containing silane-treated hydrated inorganic fillers
by the use of a lubricant composition comprising a fatty acid
having 8 to 25 carbon atoms and an alkylene-bis-amide wherein the
alkylene group has from 2 to 8 carbon atoms and the amide
constituent has from 8 to 25 carbon atoms, such lubricant
composition, preferably used in combination with antimony trioxide
and a halogenated flame retardant additive in addition to the
normally flame retardant hydrated alumina. Specifically, the
present composition includes the use of the above-described
lubricant composition in lieu of the normal calcium stearate
lubricant normally used in the above-described combinations. More
particularly, this invention is directed to a crosslinkable
polymeric composition comprising:
(a) a copolymer of ethylene and a vinyl ester of a C.sub.2 -C.sub.6
aliphatic carboxylic acid, a C.sub.1 -C.sub.6 alkyl acrylate or
C.sub.1 -C.sub.6 alkyl methacrylate,
(b) from 80 to 400 parts of hydrated inorganic filler per 100 parts
of copolymer,
(c) 0.4 to 8, and preferably 0.8 to 4, parts of an alkoxy silane
per 100 parts of hydrated inorganic filler, and
(d) an antiflame component containing a halogenated flame
retardant, antimony trioxide in addition to the normally flame
retardant hydrated inorganic filler, and, quite surprisingly, a
dual lubricant system comprising a fatty acid having from 8 to 25
carbon atoms and an alkylene-bis-amide wherein the alkylene group
contains from 2 to 8 carbon atoms and the amide groups contain from
8 to 25 carbon atoms.
The present invention can also be described as being concerned with
an improvement in a cross-linkable polymeric composition of the
type containing
(a) a copolymer of ethylene and a vinyl ester of a C.sub.2 -C.sub.6
aliphatic carboxylic acid, a C.sub.1 -C.sub.6 alkyl acrylate or a
C.sub.1 -C.sub.6 alkyl methacrylate, and
(b) a silane-treated hydrated inorganic filler, the concentration
of said filler being 80 to 400 parts of filler per 100 parts of
copolymer,
(c) halogenated flame retardants, and antimony trioxide
which comprises utilizing as an unusually effective flame retardant
a dual lubricant system comprising a fatty acid of from 8 to 25
carbon atoms and an alkylene-bis-amide in which the alkylene group
contains from 2 to 8 carbon atoms and the amide groups contain from
8 to 25 carbon atoms.
This invention also relates to an electrical conductor coated with
a uniinsulating layer comprising these crosslinkable polymer
compositions.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to crosslinkable polymeric
compositions comprising copolymers of ethylene and a vinyl ester of
an aliphatic carboxylic acid, an alkyl acrylate or an alkyl
methacrylate and a silane-treated hydrated inorganic filler which
when used with a dual lubricant system as described above in
combination with antimony trioxide and halogenated and
non-halogenated flame retardants possesses very high
flame-retardant characteristics. These compositions find particular
utility as wire and cable insulation.
The compositions of this invention contain, in addition to a
particular lubricant combination, one or more halogenated flame
retardants and, optionally antimony trioxide, one or more
crosslinkable or curable ethylene copolymers, one or more silanes
and one or more hydrated inorganic fillers. The copolymers, silanes
and inorganic fillers include those described in U.S. Pat. Nos.
3,832,326 and 3,922,422 of North et al., the disclosures of which
are incorporated herein by reference.
THE CROSSLINKABLE COPOLYMER COMPONENTS
The terms crosslinkable or crosslinking are ascribed their normal
art recognized meaning in the present specification, i.e., they
denote the formation of primary valence bonds between polymer
molecules.
Crosslinking can be accomplished by any of the known procedures
such as chemical means including peroxide crosslinking; by
radiation using cobalt-60, accelerators, .alpha.-rays,
.gamma.-rays, electrons, X-rays, etc.; or by thermal crosslinking.
The basic procedures for crosslinking polymers are extremely well
known to the art and need not be described here in detail.
The polymeric component of the present composition is a copolymer
of ethylene and a comonomer which may be a vinyl ester, an acrylate
or a methacrylate. The vinyl ester may be a vinyl ester of a
C.sub.2 -C.sub.6 aliphatic carboxylic acid, such as vinyl acetate,
vinyl propionate, vinyl butyrate, vinyl pentanoate or vinyl
hexanoate. The acrylates and methacrylates may be any of the
C.sub.1 -C.sub.6 alkyl esters including, for example, methyl,
ethyl, propyl, butyl, pentyl or hexyl acrylate or methacrylate. The
preferred copolymer comprising the polymeric component of this
invention is an ethylene-vinyl acetate copolymer containing about 6
to about 90%, preferably about 9 to about 40%, most preferably
about 9 to about 28%, vinyl acetate, balance ethylene.
Although little is gained, and some properties are even harmed, it
is possible to include minor proportions of other crosslinkable
polymers or copolymers in the composition of this invention.
However, ethylene copolymers, preferably, ethylene-vinyl acetate
copolymers, as described above, should comprise at least about 66%
of the total polymers present. Representative of such minor
polymeric components which can be used in such non-preferred
embodiments include polyethylene, copolymers of ethylene with
propylene, butene, the acrylates and maleates, polydimethyl
siloxane and polymethylphenylsiloxane, copolymers of vinyl acetate
with the acrylates, etc. Obviously, mixtures of these minor
polymeric components can be used.
Terpolymers of ethylene and vinyl acetate derived from, e.g., any
of the corresponding monomeric materials listed above (other than
ethylene or vinyl acetate) can be used. A representative terpolymer
would be an ethylene-vinyl acetate-vinyl maleate terpolymer.
The ethylene-vinyl acetate copolymers used in our invention
preferably have a melt index of from about 1.0 to about 20.0.
The polyethylenes useful in the present invention include
essentially all high, medium and low density polyethylenes as well
as mixtures thereof. The most preferred polyethylenes for blending
for use as uniinsulation for electrical wires and cables generally
have a density of from about 0.900 to about 0.950 gm./cc. and a
melt index of from about 1.0 to about 10.0.
Specifically, the compositions of the present invention provide a
highly flame retardant composition surprisingly by use of a dual
lubricant combination while retaining other desireable
characteristics including an unexpected balance of:
1. low temperature brittleness, i.e., the composition will not
readily crack during low temperature movement (ASTM D 746).
2. heat resistance after aging, i.e., excellent elongation after
extended service at 90.degree. C. and even 125.degree. C.
3. arcing and tracking resistance, as high as 5 KV, whereas even
porcelain shows surface breakdown at 4 KV. This property is not
often required, however, in the preferred environment of under 600
volt service.
4. moisture resistance, i.e., low mechanical absorption of water
which yields a superior dielectrical constant.
5. resistance to industrial chemicals.
6. resistance to oil and gasoline or diesel fuels.
It is not known why the compositions of this invention provide such
a superior balance of properties. It is possible that there is some
synergistic relationship between the ethylene-vinyl acetate
copolymer, silane and hydrated inorganic filler, but there is no
intention to be bound by such a theory. However, it has been
established that for low voltage environments, less than 5000
volts, even more particularly for less than 600 volt environments,
the compositions of this invention are particularly useful for
service as uniinsulation. Uniinsulation is an art accepted term
denoting insulation where one layer is extruded around the
conductor, and this one layer serves as the electrical insulation
and the jacketing to provide physical and flame protection. The
present compositions are especially adapted for service as
uniinsulation in the under 5000 volt range, and most especially in
the under 600 volt range, where only a single extruded coating is
used, and it is in this environment that a superior balance of
properties is required. It has been further found that
ethylene-vinyl acetate copolymers will hold very large amounts of
filler and still provide high flexibility and a high degree of
crosslinking. The simultaneous achievement of high filler loading,
flexibility and crosslinking is quite surprising as high
flexibility and high crosslinking were generally believed
incompatible, as are high crosslinking and high filler loading
(which implies low crosslinkable polymer content). Ethylene-vinyl
acetate copolymers further provide superior fire retardancy to the
polymeric compositions of the present invention.
The above described ethylene-vinyl acetate copolymers may be
crosslinked by irradiation with high-energy electron beams or
through the use of chemical crosslinking additives. Fully
crosslinked, these polymers become thermoset in behavior. In the
preferred compositions of this invention, chemical crosslinking is
preferred, particularly where superior physical strength is
required.
Chemical crosslinking is accomplished by incorporating a
crosslinking agent, e.g., dicumyl peroxide or alpha, alpha'
bis(t-butylperoxy) diisopropylbenzene, into the ethylene-vinyl
acetate copolymer. The peroxide is later activated during
processing to link the ethylene-vinyl acetate polymer chains into a
three-dimensional network (and other minor amounts of crosslinkable
polymer, if present).
The chemical crosslinking is carried out in accordance with
procedures well known in the art, and variations in the general
cross-linking conditions set out below will be apparent to one
skilled in the art. The present invention is moreover, not limited
to the use of tertiary organic peroxides for chemical crosslinking,
and other art recognized materials which decompose to provide free
radicals can be used. Obviously such crosslinking agents should not
be decomposed during compounding of the composition, but the
selection of acceptable cross-linking agents will be apparent to
those skilled in the art.
Generally speaking, as the amount of cross-linking agent used
increases, the degree of polymer crosslinking increases. Usually no
more than 10% (based on polymer) of the organic tertiary peroxides
need be used, with 3 to 6% being more typical values. Other
crosslinking agents may require different amounts, but these can be
readily determined. It is often advisable to avoid very low amounts
of crosslinking agents, since some loss or resistance to
deformation under sudden or continuous pressure may ensue.
Cross-linking coagents such as triallylcyanurate and the like may
also be included to increase the effectiveness of the crosslinking
agent.
The tertiary organic peroxides, as with most other chemical
crosslinking agents, are activated by heating to above their
activation temperature whereupon decomposition thereof occurs. Any
of the known procedures can be used to accomplish activation, e.g.,
high pressure steam application to the composition.
The art of radiation crosslinking is so highly developed that
little need be said with respect to such procedures. As higher
total doses of radiation are used, the degree of crosslinking
generally increases, and for preferred crosslinkings a total
radiation dose of about 5-25 megarads will be used.
Crosslinking is generally conducted at above atmospheric pressures,
e.g., on the order of 200 to 400 psi, although higher or lower
pressures may be used. Pressure is necessary when curing with steam
to obtain the required temperature for activation of the peroxide
catalyst. With high temperature gas curing, pressure is desired to
avoid porosity in the insulation. Porosity is highly undesirable in
electrical insulation since it lowers electrical insulation
properties and can cause premature failure from corona.
In general, the higher the degree of crosslinking the more
resistant the polymeric composition is to heat, moisture, chemical
reagents, changes with aging and environmental conditions, etc.,
and usually abrasion. At lower degrees of crosslinking there is
also some loss of heat resistance as well as pronounced effect on
percent elongation after aging. The exact degree of crosslinking
can, of course, be varied to take the above factors and their
effect on the final product into account. Although higher or lower
values can be used, for wire and cable insulation a crosslinking
percentange on the order of about 85-95% for ethylenevinyl acetate
is generally preferred, determined by extraction weight of soluble
components in the cross-linked polymer.
THE SILANE COMPONENT
One or more substituted silanes comprise the second essential
component of the polymeric compositions of the present
invention.
Any silane may be used in the present invention while will not
adversely affect the desired balance of properties and which will
help to bind the polymer and inorganic filler of the present
invention, provided that the silane does not make the composition
combustible and does not interfere with polymer crosslinking or
degrade during polymer processing, e.g., alkoxy and amine
silanes.
The preferred silanes used in forming the insulating compositions
are the alkoxysilanes, e.g., lower alkyl-, alkenyl-, alkynyl- and
arylalkoxysilanes as well as the lower alkyl-, alkenyl-, alkynyl,
and arylalkoxyalkoxy- or aryloxyalkylsilanes. Specific examples of
such silanes are methyltriethoxy-, methyltris (2-methoxyethoxy)-,
dimethyldiethoxy-, alkyl-trimethoxy-, vinyltris(2-methoxyethoxy)-,
phenyl-tris(2-methoxyethoxy), vinyltrimethoxy- and
vinyltriethoxysilane.
It is preferred to use the vinylsilanes for best results, and of
the vinylsilanes the following are especially preferred:
##STR1##
THE HYDRATED INORGANIC FILLER COMPONENT
The fillers used in the present invention are the hydrated
inorganic fillers, e.g., hydrated aluminum oxides (Al.sub.2
O.sub.3.3H.sub.2 O or Al(OH).sub.3), hydrated magnesia, hydrated
calcium silicate. Of these compounds, the most preferred is
hydrated aluminum oxide.
To obtain the superior balance of properties described, it is
mandatory that a hydrated inorganic filler be used in formulating
the polymeric compositions It must be emphasized that large
proportions of another type of filler, be it inert or not, cannot
be added to the compositions and still achieve the superior balance
of properties.
The water of hydration in the inorganic filler must be released
during the application of heat sufficient to cause combustion or
ignition of the ethylene-vinyl acetate copolymer. The water of
hydration chemically bound to the inorganic filler is released
endothermically. It has been found that the hydrated inorganic
filler increased flame retardance in a manner far superior to other
fillers previously used by the art to provide insulation with flame
retardance, e.g., carbon black, clays, titanium dioxide, etc. What
is even more surprising is that flame retardance is combined with
excellent electrical insulation properties at the high filler
loadings used, since at these loadings the copolymeric composition
contains a large amount of bound water.
The filler size should be in accordance with those sizes used by
the prior art.
THE ANTIOXIDANT COMPONENT
An antioxidant composition which can also be included as a
component of the polymeric compositions of the present invention
includes a diester of thiodipropionic acid, the preferred diester
being distearyl-3, 3' thiodipropionate (DSTDP). It has been found
that the use of two different types of antioxidants provides
effective oxidation inhibition. Thus, a mixture of an antioxidant
of the chain breaking type and one which is a peroxide decomposer
provides a very effective antioxidant composition. Therefore, with
DSTDP, which is a known peroxide decomposer, an amine or a hindered
phenol may be effectively employed as an antioxidant composition.
Among these free radical scavengers, the stearically hindered
phenols are especially effective. Useful phenols include the
alkylated phenols, the alkylidene-bis-alkylated phenols and the
polyphenols. Specific examples thereof include 2,6 ditertiary
butyl-para-cresol, octadecyl
3,5-di-t-butyl-4-hydroxyhydrocinnamate, 2,2'-methylene
bis(6-t-butyl-4-methyl phenol), 4,4'-butylidene bis (6-t-butyl-3
methyl phenol), 1,3,5-trimethyl-2,4,6-tris
(3,5-di-t-butyl-4-hydroxybenzyl) benzene and tetrakis (methylene
(3,5-di-t-butyl-4-hydroxy-hydrocinnamate) methane with the latter
being particularly preferred.
THE LUBRICANT COMPONENT
When polymeric insulation is formed on conductors by extrusion, it
is preferred that a lubricant form a portion of the insulating
composition. Such lubricants as a fatty acid soap or a metallic
derivative thereof have been used heretofore. The lubricant not
only aids in the extrusion process but it also improves the
stripping properties of wire insulation thereby facilitating the
task of the end-user.
The lubricant component comprises an essential component of the
polymeric compositions of this invention. It has been found that
the combination of antimony trioxide and halogenated flame
retardant in addition to the hydrated filler in the required
concentration, plus a particular two component lubricant
composition provided in a lubricating effective amount,
unexpectedly provides the crosslinked compositions of the present
invention with exceptionally good flame-retardant properties.
Calcium stearate has often been employed heretofore as a lubricant
for polymeric compositions such as those of North et al. Now,
however, it has been found that a lubricant composition comprising
a fatty acid such as lauric acid and a alkylene-bis-amide such as
ethylene-bis-stearamide, especially when used in combination with
antimony trioxide and halogenated and non-halogenated flame
retardants, will produce a crosslinked composition with
significantly enhanced flame retardant properties.
The dual lubricant composition of the present invention comprises a
fatty acid of from 8 to 25 carbon and an alkylene-bis-amide having
the general formula: ##STR2## wherein R=a divalent alkylene radical
of from 2 to 8 carbon atoms; and
R'= ##STR3##
wherein R.sup.2 is an aliphatic radical having from 8 to 25 carbon
atoms,
in a proportion of from about 1:1 to about 1:6 of fatty acid to
alkylene-bis-amide, and preferably in a proportion of about 1:3
acid to alkylene-bis-amide. Preferably the dual lubricant
composition comprises 25 percent lauric acid and 75 percent
ethylene-bis-stearamide. The total amount of dual lubricant
composition should be from about 0.01 to about 10 percent by weight
of the total polymeric composition, and preferably from about 0.5
to about 3 percent.
OTHER FLAME RETARDANT COMPONENTS
It has been found that the dual component lubricant composition is
especially effective in a peroxide curable polymeric composition
when used in combination with antimony trioxide, and halogenated
flame retardants such as ethylene-bis-tetra-bromophthalimide,
deca-bromodiphenyl oxide, etc. The antimony trioxide is included in
an amount of from about 2 to about 20 percent by weight and
preferably from about 4 to about 8 percent by weight, and the
halogenated flame retardant is included in an amount of from about
5 to about 30 percent by weight, and preferably from about 8 to
about 14 percent by weight of the total polymeric composition.
THE PROPORTION OF THE OTHER COMPONENTS
The amounts of polymer and filler in the composition of this
invention can be varied within the wide proportions. The silane
percentage should be in the range of from about 0.5 to 5.0 parts
per 100 parts of polymer. Lower amounts may be insufficient to
provide adequate surface treatment while larger quantities could
have an adverse effect on some of the physical properties, i.e.,
elongation, of an extruded insulating compound after
crosslinking.
Best results are obtained in coating, e.g., extruding, onto
electrical wires and cables when from 80 to 400 or more weight
parts of filler (most preferable at least 125-150 weight parts),
0.5 to 5.0 weight parts of silane and 100 weight parts of polymer
are present.
The composition of the present invention may be formed in a number
of ways. However, in every instance it is necessary that the filler
and polymer be in intimate contact with the silane when dispersion
of the filler in the polymer is initiated. This can be done in an
internal mixer, such as a Banbury or Werner & Pfleiderer
extruder.
Any processing device known to the art which insures an intimate
mixture of the essential components may be used, provided the
silane couples the hydrated inorganic filler to the polymeric
component.
It will be apparent that in addition to the essential components of
the compositions of this invention, other additives may be present,
e.g., pigments, stabilizers, so long as they do not interfere with
crosslinking, when desired, or harm desired properties. Such
materials are present in very minor proportions, ranging from less
than 10% of the polymer, and usually in amounts of less than 5%.
There are two reasons amounts of other components are not
desirable; firstly, the present composition per se has such
superior properties; secondly, any significant amounts of other
fillers for example, serve only to degrade or upset the balance or
properties.
For the formation of insulation on conductors by extrusion, a
lubricant such as a fatty acid soap or metallic derivative thereof
has in the past been utilized with success. Such materials have
also improved the stripping properties of wire insulation and
thereby permit the insulation to be easily stripped from the wire
by the user to facilitate splicing and to make terminations. It has
been the practice to use acceptable soaps such as the alkaline
earth metal fatty acid soaps, a preferred soap being calcium
stearate. Additional representative examples of such lubricants
include the alkaline earth metal salts and aluminum salts of
stearic acid, oleic acid, palmitic acid and other fatty acids used
by the art for this purpose, silicone oil, long chain aliphatic
amides, waxes, etc. Now, however, it has been discovered that the
dual lubricant system of the present invention serves not only as
an effective lubricant but also enhances flame retardant
properties, especially when used with a halogenated flame
retardant, antimony trioxide, and a non-halogenated flame retardant
in a peroxide curable polymeric composition.
The following examples are provided to further illustrate certain
aspects of the invention.
A number of crosslinkable polymeric compositions shown in Table 1
below are prepared in which the lubricant used was calcium
stearate. (The numbers in the tables indicate parts by weight).
Each of these compositions were extruded onto 14 AWG wire and
subjected to Underwriters Laboratories Flame Retardant VW-1
(Vertical-Wire) test (UL FR-1).
The results of the UL FR-1 tests conducted on the samples which
included calcium stearate are shown on Table II.
TABLE I
__________________________________________________________________________
Sample No. 1 2 3 4 5 6 7 8 9 10
__________________________________________________________________________
UE630 100 100 100 100 80 95 80 95 100 100 Ey904 0 0 0 0 20 5 20 5 0
0 Hydrated 100 100 100 100 100 100 100 100 125 125 Alumina Silane
A-172 2 2 2 2 2 2 2 2 2 2 Aegerite MA 2 2 2 2 2 2 2 2 2 2
Antioxidant Saytex BT93 30 30 0 0 30 30 30 30 30 20 Brominated
Flame-Retardant FR300BA 0 0 30 30 0 0 0 0 0 0 Deca Bromodiphenyl
Oxide Flame- Retardant Thermogard CPA 15 6 15 6 15 15 6 6 15 10
Calcium Stearate 2 2 2 2 2 2 2 2 2 2 Lauric Acid 0 0 0 0 0 0 0 0 0
0 Ethylene-bis- 0 0 0 0 0 0 0 0 0 0 Stearamide Vulcup 40KE 4.25
4.25 4.25 4.25 4.25 4.25 4.25 4.25 4.25 4.25 (Peroxide) Sb.sub.2
O.sub.3 0 0 0 0 0 0 0 0 0 0
__________________________________________________________________________
Sample No. 11 12 13 14 15 16 17 18 19
__________________________________________________________________________
UE630 100 100 100 100 100 100 100 100 100 Ey904 0 0 0 0 0 0 0 0 0
Hydrated 125 100 0 0 0 100 100 100 100 Alumina Silane A-172 2 2 2 2
2 2 2 2 2 Aegerite MA 2 2 2 2 2 2 2 2 2 Antioxidant Saytex BT93 20
20 30 0 30 15 15 30 30 Brominated Flame-Retardant FR300BA 0 0 0 30
0 0 0 0 0 Deca Bromodiphenyl Oxide Flame- Retardant Thermogard CPA
6 15 15 15 6 5 15 15 15 Calcium Stearate 2 2 2 2 2 2 2 2 2 Lauric
Acid 0 0 0 0 0 0 0 0 0 Ethylene-bis- 0 0 0 0 0 0 0 0 0 Stearamide
Vulcup 40KE 4.25 4.25 4.25 4.25 4.25 4.25 4.25 4.25 4.25 (Peroxide)
Sb.sub.2 O.sub.3 0 0 0 0 0 0 0 0 0
__________________________________________________________________________
TABLE II
__________________________________________________________________________
Ave Seconds Sample Remains in Flame Test Thickness 1st 2nd 3rd 4th
5th Glowing Flag Cotton Pass/ Sample in .mu. Burn Burn Burn Burn
Burn Particles Burn Burn Fail
__________________________________________________________________________
1 98 0 5 0 0 0 Yes No Yes Fail 0 0 28 0 0 Yes No Yes 0 23 0 0 0 No
No No 2 103 0 30 0 0 0 No No No Fail 0 0 2 0 0 Yes No Yes 2 2 7 0 0
Yes No Yes 3 97 15 0 0 0 0 Yes No Yes Fail 15 3 0 0 0 Yes No Yes 0
0 0 0 0 Yes No Yes 4 98 7 0 20 0 0 Yes No Yes Fail 20 0 0 0 0 Yes
No Yes 33 5 0 0 0 No No No 5 103 0 9 3 0 0 No No No Pass 0 16 0 0 0
No No No 0 4 3 0 0 No No No 6 102 0 6 0 0 0 No No No Fail 0 0 3 0 0
Yes No Yes 0 21 0 0 0 No No No 7 103 0 0 4 0 0 Yes No Yes Fail 0 10
0 0 0 No No No 0 0 4 0 0 Yes No Yes 8 108 2 0 6 0 0 Yes No Yes Fail
0 0 20 0 0 Yes No Yes 0 7 8 0 0 Yes No Yes 9 95 0 2 0 0 0 No No No
Fail 0 15 6 0 0 Yes No Yes 0 6 3 0 0 No No No 10 98 7 5 0 0 0 Yes
No Yes Fail 10 4 5 0 0 Yes No Yes 0 3 0 0 0 Yes No Yes 11 99 0 4 2
0 0 Yes No Yes Fail 65 0 0 0 0 No No No 62 0 0 0 0 No No No 12 99 0
0 4 0 0 Yes No Yes Fail 0 0 0 0 0 Yes No Yes 0 0 95 0 0 Yes Yes Yes
13 98 5 5 0 0 0 Yes No Yes Fail 10 0 0 0 0 Yes No Yes 0 0 104 0 0
Yes Yes Yes 14 96 22 15 5 0 0 No No No Fail 0 88 0 0 0 Yes Yes Yes
0 0 0 0 0 Yes No Yes 15 95 62 0 0 0 0 No No No Fail 0 23 0 0 0 No
No No 34 4 0 0 0 Yes No Yes 16 100 10 10 7 0 0 Yes No Yes Fail 10
10 3 0 0 Yes No Yes 15 16 0 0 0 Yes No Yes 17 97 110 0 0 0 0 No Yes
No Fail 0 10 9 0 0 Yes No Yes 10 6 5 0 0 Yes No Yes 18 100 0 35 0 0
0 No No No Fail 0 35 0 0 0 No No No 0 45 0 0 0 Yes No Yes 19 101 0
35 0 0 0 No No No Pass 0 8 0 0 0 No No No 0 13 0 0 0 No No No
__________________________________________________________________________
The "Yes" in the last three columns indicates that the insulation
materia did produce the result described, e.g., yes indicates that
glowing particles were produced, that the cotton base was burned,
and that the insulation did burn up the wire to the "flag".
As can be seen from the results of the tests, only two samples,
Nos. 5 and 19, containing calcium stearate passed the UL FR-1 flame
retardancy test. This performance is not considered satisfactory.
Although the two materials passed the test, their similarity in
formulation to other materials indicates reproducible passage of
the FR-1 Test would be very poor and not acceptable for commercial
utilization.
Further samples were prepared utilizing a dual component lubricant
in combination with the halogenated flame-retardant and antimony
trioxide as shown in Table III.
TABLE III
__________________________________________________________________________
Sample No. 20 21 22 23 24 25 26 27 28 29 30
__________________________________________________________________________
UE630/631 100 95 100 100 100 100 100 80 80 100 100 Ey904 0 5 0 0 0
0 0 20 20 0 0 Hydrated 100 100 100 100 100 100 100 100 100 100 100
Alumina Silane A-172 2 2 2 2 2 2 2 2 2 2 2 Aegerite MA 2 2 2 2 2 2
2 2 2 2 2 Antioxidant Saytex BT93 30 30 30 0 30 30 0 30 0 30 25
FR300BA 0 0 0 30 0 0 30 0 30 0 0 Thermogard CPA 15 15 15 15 15 0 0
15 15 10 12.5 Ca Stearate 0 0 0 0 0 0 0 0 0 0 0 Lauric Acid 0.125
0.125 0.125 0.125 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Ethylene-bis-
0.375 0.375 0.375 0.375 0.75 0.75 0.75 0.75 0.75 0.75 0.75
Stearamide Vulcup 90KE 4.25 4.25 4.25 4.25 4.25 4.25 4.25 4.25 4.25
4.25 4.25 Sb.sub.2 O.sub.3 0 0 0 0 0 15 15 0 0 0 0
__________________________________________________________________________
The UL FR-1 test was conducted on the samples which contained the
dual lubricant system, the results of which are shown in Table
IV.
TABLE IV
__________________________________________________________________________
Seconds Sample Ave Remains in Flame Test Thickness 1st 2nd 3rd 4th
5th Glowing Flag Cotton Pass/ Sample in .mu. Burn Burn Burn Burn
Burn Particles Burn Burn Fail
__________________________________________________________________________
20 103 0 9 3 0 0 No No No Pass 0 16 0 0 0 No No No 0 4 3 0 0 No No
No 21 99 0 0 6 0 0 No No No Fail 0 3 0 0 0 Yes No Yes 0 0 30 0 0 No
No No 22 95 0 6 0 0 0 No No No Pass 0 23 0 0 0 No No No 0 15 0 0 0
No No No 23 94 0 3 0 0 0 Yes No Yes Fail 0 33 0 0 0 Yes No Yes 0 38
0 0 0 Yes No Yes 24 97 0 3 0 0 0 No No No Pass 0 2 16 0 0 No No No
0 3 0 0 0 No No No 25 105 0 25 0 0 0 No No No Pass 0 19 0 0 0 No No
No 0 6 0 0 0 No No No 26 97 0 18 0 0 0 Yes No Yes Fail 0 31 0 0 0
Yes No Yes 0 6 0 0 0 Yes No Yes 27 90 0 0 0 0 0 No No No Pass 0 22
0 0 0 No No No 0 16 0 0 0 No No No 28 97 0 5 0 0 0 No No No Pass 0
26 0 0 0 No No No 0 15 0 0 0 No No No 29 100 0 12 0 0 0 Yes No Yes
Fail 0 34 0 0 0 Yes No Yes 0 38 0 0 0 Yes No Yes 30 98 0 12 0 0 0
Yes No Yes Fail 0 50 0 0 0 Yes No Yes 0 40 0 0 0 Yes No Yes
__________________________________________________________________________
It can be seen from these results that even under the stringent
FR-1 test, the samples having compositions which include the dual
lubricant system pass over 50% of the time whereas the samples
without the dual lubricant system passed only 18% of the time.
Moreover, samples 22-30 which include the dual lubricant
composition, when compared to sample 18 and 19 of which contain
calcium stearate as a lubricant, can be seen to retain other
desirable characteristics such as physical strength and elongation
capabilities as shown in Table V.
TABLE V
__________________________________________________________________________
Sample No. 18 19 22 23 24 25 26 27 28 29 30
__________________________________________________________________________
Tensile Strength, psi 1880 1850 2110 2470 2180 2120 2250 1920 2070
2130 2230 Elongation, % 210 240 200 230 200 200 230 260 260 200 210
After 7 Days @ 158.degree. C. Tensile Strength, psi 2060 1980 2150
2500 2280 2120 2230 2040 2150 2040 2260 Elongation, % 150 160 160
170 150 140 160 190 190 120 150
__________________________________________________________________________
While there have been described what are presently believed to be
the preferred embodiments of the invention, those skilled in the
art will realize that changes and modifications may be made thereto
without departing from the spirit of the invention, and it is
intended to claim all such changes and modifications as fall within
the true scope of the invention.
* * * * *